苏鲁超高压变质岩的构造热历史:中国大陆科学钻探工程(CCSD)主孔(MH)和先导孔(PP2)的磷灰石裂变径迹约束  

Thermotectonic history of Sulu UHP metamorphic rock:Apatite fission track constraints from MH and PP2 of CCSD.

作　　者：刘顺生[1] GLASMACHER Ulrich 许志琴[4] WEBER Ursula WAGNER Günther JONCKHEERE Raymond 殷秀兰[5] 

机构地区：[1]中国科学院广州地球化学研究所,广州510640 [2]Max-Planck-Institut für Kernphysik [3]Ruprecht-Karls Universitt Heidelberg [4]中国地质科学院地质研究所,北京100037 [5]中国地质科学院地质力学研究所,北京100081

出　　处：《岩石学报》2009年第7期1612-1618,共7页Acta Petrologica Sinica

基　　金：国家" 973 "项目(2003CB716502)资助成果

摘　　要：本文包括中国大陆科学钻(CCSD)主孔(MH)0～5000m和先导孔(PP2)0～1000m的磷灰石裂变径迹分折结果,先导孔PP2的裂变径迹表观年龄变化范围为79.5±5.1～50.4±6.2Ma,主孔的裂变径迹表观年龄变化范围为98.6±17.0～2.9±2.0Ma,主孔在4200m以下,磷灰石样品中实际上已不存在自发裂变径迹,表明裂变径迹时钟已经"置零"。实验资料表明,裂变径迹表观年龄值随样品深度的增加而逐渐减少,直到一定深度,即达到磷灰石的裂变径迹封闭温度(～120℃)以后,年龄值为零。根据主孔0～2000m和先导孔0～1000m的裂变径迹年龄剖面,作为一级近似,计算出超高压变质岩体在90～30Ma期间,平均隆升速度为～35m/Ma。对主孔测定了9个样品的约束径迹(Confined track)长度,样品约束径迹平均长度的变化范围约为13.1μ7.4μm,总的变化趋势是:约束径迹平均长度随样品深度的增加而逐渐减少。样品的约束径迹长度分布都具有双峰型特征。根据裂变径迹年龄和约束径迹长度的资料,应用计算机模拟得到了样品的时间-温度(t-T)轨迹。结果表明,岩体从早白垩世(～120Ma)快速冷却以后,在晚白垩世和始新世又经历了两次加热作用,始新世末岩体所达到的温度大约是80℃,随后岩体则一直上升和缓慢冷却到现今所处的位置。在最后～30Ma岩体的平均隆升速度为～53m/Ma。This study reports on a fission track analysis of core samples from 0 to 5000m depth in the main hole (MH) and 0 similar to 1000m depth in the pilot PP2 of the Chinese Continental Scientific Drilling ( CCSD) project. We determined the fission track ages of 59 apatite samples from different depths. The ages range between 79.5 +/- 5.1 and 50.4 +/- 6.2Ma for PP2 and between 98.6 +/- 17.0 and 2.9 +/- 2.0Ma for MH, and the values of age show a general decreasing trend with depth, from 87.1 +/- 11.2Ma at the surface to 2.9 +/- 2.0Ma at 4106m depth. As a first approximation, an average uplift rate of similar to 35m/Ma is calculated for the period 90 similar to 30Ma. The variation of ages, however, has some fluctuation reflecting tectonic complexities. It is inferred that there are some normal faults and reverse faults. Modeling of t-T paths based on confined track-lengths and fission track ages reveals the likelihood of reheating during the Late Cretaceous and Eocene, following by cooling to similar to 80 degrees C during Eocene and similar cooling until the samples reached their present-day position in the Donghai area.

关 键 词：中国大陆科学钻探工程 裂变径迹年龄测定 热年代学 超高压变质带 磷灰石 东海 

分 类 号：P597.1[天文地球—地球化学]